Hi,
I have a quick question. I want to simulate a keyboard with my arduino and I'm wondering if i can at the same time use RX or TX pins as inputs for the button. I know that you can't use them when using serial communication but is it the same when using keyboard library?
Thank you in advance for your answer 
Which Arduino?
pro micro 3,3v 8000 MHz
Sorry, I am not familiar with that one and I can't find it on this website. Is it listed here and I can't see it or is it from somewhere else?
I have a chinese copy of this Pro Micro - 3.3V/8MHz - DEV-12587 - SparkFun Electronics
That should be an atmega32u4, Rx and Tx are Serial1, USB is Serial, separate serial ports, and can be used at the same time.
lolotoster:
pro micro 3,3v 8000 MHz
You mean 8MHz. 8000MHz, or 8GHz, would be amazing, maybe one day!
Yes, on micro you can use Tx, Rx pins for ordinary digital inputs/outputs, or use them for connecting components that use serial communications, like a GPS module. They are not needed for uploading your sketch or using Serial Monitor.
You can't do that with Uno, Nano, Pro Mini... that's why it's important to remember to say what type of Arduino you have in your first post.
I disagree that you can't use RX & TX at all because they are used by some system means - this is how I understand reading this topic. I managed to get RX & TX working as digital outputs by disabling specific serial connections. I mean removing Serial.begin(9600) code and running in release mode (both debug & tests disabled). And keep connecting through USB for power. My board is Arduino Uno R3. Will try those pins for input later (to use for keypad connection)